Method of producing positive electrode active material for nonaqueous electrolyte secondary battery

ABSTRACT

A method of producing a positive electrode active material for a nonaqueous electrolyte secondary battery, the method includes preparing nickel-containing composite oxide particles having a ratio  1 D 90 / 1 D 10  of a 90% particle size  1 D 90  to a 10% particle size  1 D 10  in volume-based cumulative particle size distribution is 3 or less; mixing the composite oxide particles and a lithium compound to obtain a first mixture; subjecting the first mixture to a first heat treatment at a first temperature and a second heat treatment at a second temperature higher than the first temperature to obtain a first heat-treated product; and subjecting the first heat-treated material to a dispersion treatment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of copending U.S. application Ser. No.16/404,287, filed on May 6, 2019, which is a Divisional of copendingU.S. application Ser. No. 16/140,976, filed on Sep. 25, 2018 (Issued asU.S. Pat. No. 10,326,132 on Jun. 18, 2019), which is a Divisional ofU.S. application Ser. No. 15/473,974, filed on Mar. 30, 2017 (Issued asU.S. Pat. No. 10,115,967 on Oct. 30, 2018), which claims the benefitunder 35 U.S.C. § 119(a) to Japanese Patent Application No. 2016-072487,filed on Mar. 31, 2016, and Japanese Patent Application No. 2017-059653,filed on Mar. 24, 2017, the disclosures of which are hereby incorporatedby reference in their entirety.

BACKGROUND Field of the Invention

The present disclosure relates to a method of producing a positiveelectrode active material for a nonaqueous electrolyte secondarybattery.

Description of Related Art

A positive electrode active material for a nonaqueous electrolytesecondary battery for application to large-sized power machines, such aselectric vehicles, is required to have high output characteristics andhigh durability. In order to obtain high output characteristics, in apositive electrode active material having a structure in which a largenumber of primary particles are aggregated to form a secondaryparticles, it is effective, for example, to have a hollow structure ineach secondary particle to increase the BET specific surface area, andto reduce the size of aggregated primary particles of each secondaryparticle. However, in such a positive electrode active material, one ormore cracks may occur in the secondary particles due to pressurizationin the formation of an electrode, expansion/shrinkage upon charge anddischarge, etc., and there has been room for improvement in durability.

In relation to the above problems, a positive electrode active materialcontaining lithium-transition metal oxide particles composed of a singleparticle or composed of a reduced number of primary particles formingeach secondary particle and a method of producing the same are proposed,in which a lithium-transition metal composite oxide including aggregatedsecondary particles is ground to adjust the particle size of secondaryparticles, and the lithium-transition metal composite oxide after theparticle size adjustment is subjected to another heat treatment (see,e.g., JP 2001-243949 A).

SUMMARY

A method of producing a positive electrode active material for anonaqueous electrolyte secondary battery, the method includes preparingnickel-containing composite oxide particles having a ratio ¹D₉₀/¹D₁₀ ofa 90% particle size ¹D₉₀ to a 10% particle size ¹D₁₀ in volume-basedcumulative particle size distribution of 3 or less; mixing the compositeoxide particles and a lithium compound to obtain a first mixture;subjecting the first mixture to a first heat treatment at a firsttemperature and a second heat treatment at a second temperature higherthan the first temperature to obtain a first heat-treated material; andsubjecting the first heat-treated material to a dispersion treatment.The positive electrode active material includes lithium-transition metalcomposite oxide particles has a ratio ²D₅₀/²D_(SEM) of a 50% particlesize ²D₅₀ in volume-based cumulative particle size distribution to anaverage particle size ²D_(SEM) based on electron microscopic observationin a range of 1 to 4. The lithium-transition metal composite oxideparticles have a composition represented by the following formula (1):

Li_(p)Ni_(x)Co_(y)M¹ _(z)O_(2+α)  (1)

In formula, 1.0≤p≤1.3, 0.3≤x<0.6, 0≤y≤0.4, 0≤z≤0.5, x+y+z=1, and−0.1≤α≤0.1, and M¹ represents at least one of Mn and Al.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 1.

FIG. 2 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 3.

FIG. 3 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 4.

FIG. 4 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Example 5.

FIG. 5 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Comparative Example 1.

FIG. 6 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Comparative Example 2.

FIG. 7 shows an example of an SEM image of lithium-transition metalcomposite oxide particles in Comparative Example 3.

DETAILED DESCRIPTION

The present invention resides in an efficient method of producing apositive electrode active material containing lithium-transition metaloxide particles composed of a single particle or composed of a reducednumber of primary particles forming each secondary particle.

The invention is described in detail as follows, and includes theaspects shown below.

A method of producing a positive electrode active material for anonaqueous electrolyte secondary battery includes: preparingnickel-containing composite oxide particles having a ratio ¹D₉₀/¹D₁₀ ofa 90% particle size ¹D₉₀ to a 10% particle size ¹D₁₀ in volume-basedcumulative particle size distribution of 3 or less; mixing the compositeoxide particles and a lithium compound to obtain a first mixture;subjecting the first mixture to a first heat treatment at a firsttemperature and a second heat treatment at a second temperature higherthan the first temperature to obtain a first heat-treated material; andsubjecting the first heat-treated material to a dispersion treatment.The positive electrode active material includes lithium-transition metalcomposite oxide particles having a ratio ²D₅₀/²D_(SEM) of a 50% particlesize ²D₅₀ in volume-based cumulative particle size distribution to anaverage particle size ²D_(SEM) based on electron microscopic observationin a range of 1 to 4. The lithium-transition metal composite oxideparticles have a composition represented by the following formula (1):

Li_(p)Ni_(x)Co_(y)M¹ _(z)O_(2+α)  (1)

in formula (1), 1.0≤p≤1.3, 0.3≤x<0.6, 0≤y≤0.4, 0≤z≤0.5, x+y+z=1, and−0.1≤α≤0.1, and M¹ represents at least one of Mn and Al.

According to one embodiment of the present disclosure, an efficientproduction method for obtaining a positive electrode active materialcontaining lithium-transition metal oxide particles composed of a singleparticle or composed of a reduced number of primary particles formingeach secondary particle, can be provided.

A method of producing a positive electrode active material for anonaqueous electrolyte secondary battery according the presentdisclosure will be described below based on embodiments Hereinafter, amethod for producing a positive electrode active material for anonaqueous electrolyte secondary battery according the presentdisclosure will be described based on embodiments. Embodiments in thebelow are intended to embody the technical concept of the presentinvention, and the scope of the present invention is not limitedthereto. In the present specification, the content of each component ina composition refers to, in the case where a plurality of substancescorresponding to such a component are present in the composition, refersto the total amount of the plurality of substances present in thecomposition unless otherwise specified.

Method for Producing Positive Electrode Active Material for NonaqueousElectrolyte Secondary Battery

A method for producing a positive electrode active material for anonaqueous electrolyte secondary battery, the method includes preparingnickel-containing composite oxide particles (hereinafter sometimesreferred to as “first composite oxide particles”) having a ratio¹D₉₀/¹D₁₀ of a 90% particle size ¹D₉₀ to a 10% particle size ¹D₁₀ involume-based cumulative particle size distribution of 3 or less; mixingthe composite oxide particles and a lithium compound to obtain a firstmixture; subjecting the first mixture to a first heat treatment at afirst temperature and a second heat treatment at a second temperaturehigher than the first temperature to obtain a first heat-treatedmaterial; and subjecting the first heat-treated material to a dispersiontreatment. The obtained positive electrode active material includeslithium-transition metal composite oxide particles that have a ratio²D₅₀/²D_(SEM) of a 50% particle size ²D₅₀ in volume-based cumulativeparticle size distribution to an average particle size ²D_(SEM) based onelectron microscopic observation in a range of 1 to 4. Thelithium-transition metal composite oxide has a composition representedby the following formula (1):

Li_(p)Ni_(x)Co_(y)M¹ _(z)O_(2+α)  (1)

In formula (1), 1.0≤p≤1.3, 0.3≤x<0.6, 0≤y≤0.4, 0≤z≤0.5, x+y+z=1, and−0.1≤α≤0.1, and M¹ represents at least one of Mn and Al.

The first composite oxide particles having a uniform particle sizehaving ¹D₉₀/¹D₁₀ of 3 or less are used as a raw material, and theparticles are heat-treated together with a lithium compound, followed byperforming a dispersion treatment instead of a grinding treatment,lithium-transition metal composite oxide particles that are made of asingle primary particle or a secondary particle composed of a smallnumber of primary particles (hereinafter both may be simply referred toas “a single particle”) are efficiently produced. In a conventionalmethod of producing a positive electrode active material includingsimple particles, the particle size is adjusted by grinding, with whichcontrol of the particle size distribution may be difficult, and it maybe particularly difficult to obtain a sharp particle size distributionwith a uniform particle size.

The first composite oxide particles for use in the method of producing apositive electrode active material contains at least nickel, and it ispreferable that nickel and at least one element selected from the groupconsisting of cobalt, manganese, and aluminum be contained, and it ismore preferable that nickel, cobalt, and at least one of manganese andaluminum be contained.

In the first composite oxide particles, ¹D₉₀/¹D₁₀ is 3 or less, andpreferably 2 or less. In the first composite oxide particles, the 50%particle size ¹D₅₀ in volume-based cumulative particle size distributionis 12 μm or less, for example, preferably 6 μm or less, and morepreferably 4 μm or less, and is 1 μm or more, for example, andpreferably 2 μm or more.

In the case where the first composite oxide particles contain nickel,cobalt, and at least one of manganese and aluminum, the content ratioNi/Co/(Mn+Al) of nickel, cobalt, and manganese+aluminum may be 1/1/1 or1/1/(0.5/0.5) on a molar basis, for example.

The first composite oxide particles may be prepared by suitableselection from commercially available products, or may also be preparedby producing particles having desired characteristics. In the case wherethe first composite oxide particles are produced, for example, the firstcomposite oxide particles by subjecting a composite hydroxide containingdesired metal elements to a heat treatment. The composite hydroxide maybe produced by a coprecipitation method, in which a raw materialcompound soluble in a solvent is dissolved in the solvent, and thetemperature is controlled, the pH is adjusted, or a complexing agent isadded, for example, to obtain a composite hydroxide according to theintended composition. For the details of the method for obtaining acomposite oxide by a coprecipitation method, JP 2003-292322 A, JP2011-116580 A, and the like (the disclosures of which are incorporatedherein by reference in their entirety) may be referred to.

The prepared first composite oxide particles are mixed with a lithiumcompound to prepare a first mixture. Examples of lithium compoundsinclude lithium hydroxide, lithium carbonate, and lithium oxide.

The particle size of the lithium compound used is, as the 50% particlesize in volume-based cumulative particle size distribution, in a rangeof 0.1 μm to 100 μm, for example, preferably 2 μm to 20 μm.

In the first mixture, the ratio of the total number of moles of lithiumto the total number of moles of metal elements forming the firstcomposite oxide particles is in a range of 1 to 1.3, for example,preferably 1 to 1.25.

The first composite oxide particles and a lithium compound may be mixedusing a high-speed shear mixer or the like.

The obtained first mixture is subjected to a first heat treatment at afirst temperature and then to a second heat treatment at a secondtemperature higher than the first temperature, so that a firstheat-treated material is obtained. Performing heat-treatment of thefirst mixture in two stages, that is, a first heat treatment at arelatively low temperature and a second heat treatment at a relativelyhigh temperature, allows for, for example, in the first heat treatment,proceeding the reaction between the lithium compound and the firstcomposite oxide can proceed sufficiently to reduce the residual lithiumcompound at a temperature in a region where conversion into simpleparticles does not occur, and in the second heat treatment, growingparticles grow while suppressing the sintering of particles due toaction of the residual lithium compound as a flux.

In the heat treatment of the first mixture, for example, the firstmixture is heated from room temperature to the first temperature andheat-treated at the first temperature for a predetermined period oftime, then heated to the second temperature and heat-treated at thesecond temperature for a predetermined period of time, and cooled toroom temperature, for example; as a result, a first heat-treatedmaterial is obtained. The first heat-treated material should have beenheat-treated at two or more temperatures, and may further be subjectedto an additional heat treatment after the second heat treatment at atemperature higher than the second temperature.

The first temperature is in a range of 850° C. to 950° C. or less, forexample, preferably 900° C. to 940° C. Meanwhile, the second temperatureis in a range of 980° C. to 1,100° C., for example, preferably 1,000° C.to 1,080° C. Further, the difference between the first temperature andthe second temperature is 30° C. or more, for example, preferably 100°C. or more, and is 250° C. or less, for example, preferably 180° C. orless.

The duration of the first heat treatment is, for example, in a range of1 hour to 20 hours, preferably 5 hours to 10 hours. The duration of thesecond heat treatment is, for example, in a range of 1 hour to 20 hours,for example, preferably 5 hours to 10 hours. The duration of the firstheat treatment and the duration of the second heat treatment may be thesame or different. In the case where they are different, for example,the duration of the second heat treatment may be longer than theduration of the first heat treatment. More specifically, for example,the duration of the second heat treatment may be 1.05 to 2 times,preferably 1.1 to 1.5 times, longer than the heat treatment time of thefirst heat treatment. The first heat treatment and the second heattreatment may be successively performed, or may be each independentlyperformed. In the case where the first heat treatment and the secondheat treatment are successively performed, the heating rate from thefirst temperature to the second temperature may be 5° C./min, forexample.

The heat treatment may be performed in the air or an oxygen atmosphere.Further, the heat treatment may be performed, for example, using a boxfurnace, a rotary kiln, a pusher furnace, a roller hearth kiln, or thelike.

The first heat-treated material is subjected to a dispersion treatment.Dissociation of the sintered primary particles not by a grindingtreatment, which is accompanied by strong shear force or impact, but bya dispersion treatment, the resulting lithium-transition metal compositeoxide particles have a narrow particle size distribution and a uniformparticle size. The dispersion treatment may be performed in a drycondition or a wet condition, and is preferably performed in a drycondition. The dispersion treatment can be performed, for example, usinga ball mill, a jet mill, or the like. The conditions for the dispersiontreatment may be set, for example, so that the ²D₅₀/²D_(SEM) of thelithium-transition metal composite oxide particles after the dispersiontreatment is in a desired range, for example, in a range of 1 to 4.

For example, in the case where the dispersion treatment is performedusing a ball mill, resin media may be used. Examples of materials forthe resin media include a urethane resin and a nylon resin. Generally,alumina, zirconia, or the like is used for the material of the media fora ball mill, and particles are ground with such media. In contrast,using resin media allows for dissociating sintered primary particleswithout the particles being ground. The size of the resin media may bein a range of ϕ 5 mm to 30 mm, for example. Further, for the body(shell), a urethane resin, a nylon resin, or the like may be used, forexample. The time of the dispersion treatment is in a range of 3 minutesto 60 minutes, for example, preferably in a range of 10 minutes to 30minutes. For the conditions for the dispersion treatment using a ballmill, the amount of media, the speed of rotation or vibration, thedispersion time, the specific gravity of medium, and the like can beadjusted in accordance with the value of ¹D₉₀/¹D₁₀, etc., of the firstcomposite oxide particles serving as a raw material so as to achieve thedesired value of ²D₅₀/²D_(SEM).

For example, in the case where the dispersion treatment is preformedusing a jet mill, the feed pressure, the grinding pressure, the feedspeed, and the like can be adjusted depending on the ¹D₉₀/¹D₁₀, etc., ofthe first composite oxide particles serving as a raw material so as toachieve the desired ²D₅₀/²D_(SEM) without the primary particles beingground. The feed pressure may be in a range of 0.1 MPa to 0.5 MPa, forexample, and the grinding pressure may be in a range of 0.1 MPa to 0.6MPa, for example.

Through the production method described above, a positive electrodeactive material containing lithium-transition metal composite oxideparticles in the form of simple particles can be efficiently produced.

Certain embodiments of the production method may further include: mixingthe dispersion-treated first heat-treated material and a lithiumcompound to obtain a second mixture; and subjecting the obtained secondmixture to a heat treatment to obtain a second heat-treated material. Byadding the lithium compound a plurality of times to obtain a mixture ineach time and heat-treating each of the obtained mixtures,lithium-transition metal composite oxide particles having a narrowerparticle size distribution and a more uniform particle size tend to beobtained. The first heat-treated material contains a lithium-transitionmetal composite oxide, for example.

The details of the lithium compound in the second mixture are asdescribed above. The lithium compound contained in the second mixturemay be a single kind or a combination of two or more kinds, and may bethe same as or different from the lithium compound in the first mixture.

In the second mixture, the ratio of the total number of moles of lithiumto the total number of moles of metal elements other than lithiumforming the first heat-treated material is in a range of 1.0 to 1.3, forexample, preferably in a range of 1.08 to 1.22. In the case where thelithium compound is added in a plurality of times, in the first mixture,the ratio of the total number of moles of lithium to the total number ofmoles of metal elements contained in the first composite oxide is in arange of 0.75 to 1.27, for example, preferably in a range of 0.9 to1.07.

The first heat-treated material and the lithium compound can be mixedusing a high-speed shear mixer or the like, for example.

The obtained second mixture is subjected to a heat treatment to obtain asecond heat-treated material containing lithium-transition metalcomposite oxide particles. The temperature of the heat treatment is 650°C. or more, for example, preferably 800° C. or more, and is 970° C. orless, for example, preferably 950° C. or less. The heat treatment may beperformed at a single temperature, or may also be performed at aplurality of temperatures.

The heat treatment time of the second mixture is in a range of 1 hour to20 hours, for example, preferably in a range of 5 hours to 15 hours. Theheat treatment of the second mixture may be performed in air or anoxygen atmosphere.

The heat-treated second heat-treated material may be subjected to adispersion treatment as necessary, and the details thereof are asdescribed above. Lithium-transition metal composite oxide particlesobtained by heat-treating and dispersion-treating the second mixturehave a narrower particle size distribution, and is a positive electrodeactive material having improved output characteristics and durability.

The lithium-transition metal composite oxide particles obtained by theproduction method described above have a composition represented byformula (1) and has the ratio ²D₅₀/²D_(SEM) of the 50% particle size²D₅₀ in volume-based cumulative particle size distribution to theaverage particle size ²D_(SEM) based on electron microscopic observationin a range of 1 to 4. Further, it is preferable that the ratio ²D₉₀/²D₁₀of the 90% particle size ²D₉₀ to the 10% particle size ²D₁₀ involume-based cumulative particle size distribution be 4 or less.

²D₅₀/²D_(SEM) in a range of 1 to 4 indicates that the lithium-transitionmetal composite oxide particles are a single particle or particlescomposed of a small number of primary particles and have reduced contactgrain boundaries between primary particles. In addition, ²D₉₀/²D₁₀ of 4or less indicates that the lithium-transition metal composite oxideparticles have a narrow distribution width in volume-based cumulativeparticle size, and the particle size is uniform. A positive electrodeactive material containing lithium-transition metal composite oxideparticles and having such configurations are expected to achieve bothexcellent output characteristics and excellent durability.

As compared with a positive electrode active material containinglithium-transition metal composite oxide particles having secondaryparticles made of a large number of aggregated primary particles, in aconventional positive electrode active material containinglithium-transition metal composite oxide particles, which are singleparticles, a decrease in capacity retention ratio due to thedisconnection of the electrical conduction path of lithium ions causedby the grain boundary dissociation of secondary particles during acharge/discharge cycle is prevented, and also an increase in thediffusion/migration resistance of lithium ions is prevented.Accordingly, good durability is exhibited. Meanwhile, in such aconventional positive electrode active material, a three-dimensionalgrain boundary network as in a positive electrode active material madeof aggregated particles is hardly formed, and a high-power designutilizing grain boundary conduction is difficult to achieve. Therefore,there has been a tendency that the output characteristics areinsufficient. It is believed that output power characteristics can beincreased by decreasing the particle size (²D_(SEM)) of singleparticles. However, in the case where the particle size is too small,the interaction between particles is increased, so that the electrodeplate filling properties tend to be greatly deteriorated. Further,decrease in powder fluidity may the handling ability may greatlydeteriorated. Meanwhile, in particular, for obtaining a practical energydensity, a certain degree of the particle size is needed. However, it isbelieved that an increase in particle size tends to result in a greaterlack of output power.

The lithium-transition metal composite oxide particles according to oneembodiment of the present disclosure have more uniform particle sizethan that of conventional single particles. With this configuration,even in the case where the battery is charged and discharged at a highcurrent density, variations in charge/discharge depth among particlesdue to current concentration on some particles can be reduced.Accordingly, it is believed that, while preventing increase inresistance due to current concentration, local degradation throughcharge/discharge cycles can be reduced.

Further, with uniform particle size of lithium-transition metalcomposite oxide particles having reduced grain boundaries, the particlesdo not collapse even when pressed at a high pressure in themanufacturing of an electrode. Accordingly, the space between particlesis considered to be homogenized. In addition, in the case where abattery is formed, the space between particles is filled with anelectrolyte to serve as a lithium ion diffusion path. With uniform sizeof such a diffusion path, variations in amount of charge/discharge amongparticles can be reduced. Accordingly, it is considered that, evenlithium-transition metal composite oxide particles having reducedcontact grain boundaries between primary particles can achieve goodoutput power characteristics while ensuring electrode plate fillingperformance.

Further, generally, in the case where single particles are synthesized,heat treatment is needed to be performed under high temperature forgrowth of particles. In particular, in a composition having a high Niproportion, when calcination is performed at a high temperature, theelement Ni may be incorporated into the Li site, that is, so-calleddisorder may occur. Disorder inhibits the diffusion of Li ions incomposite oxide particles and causes resistance, resulting in effectssuch as a decrease in charge/discharge capacity at a practical currentdensity, a decrease in output characteristics, etc. Therefore, it ispreferable that such disorder be suppressed. Suppressing disorder allowsfor further improving the capacity and output power characteristics insingle particles.

In the lithium-transition metal composite oxide particles forming thepositive electrode active material, the average particle size ²D_(SEM)based on electron microscopic observation is in a range of 1 μm to 7 μmin view of durability. In view of output characteristics and theelectrode plate filling properties, the average particle size ²D_(SEM)is preferably 1.5 μm or more, and is preferably 5.5 μm or less, and morepreferably 3 μm or less.

The average particle size ²D_(SEM) based on electron microscopicobservation is determined as follows. Using a scanning electronmicroscope (SEM), observation is performed at a magnification of 1,000to 10,000 in accordance with the particle size. One hundred particleshaving recognizable profiles are selected, and the equivalent sphericaldiameters of the selected particles are calculated using an imageprocessing software. The arithmetic average of the obtained equivalentspherical diameters is determined as ²D_(SEM).

In the case where ²D₅₀/²D_(SEM) is 1, the lithium-transition metalcomposite oxide particles are single particles. In the case where²D₅₀/²D_(SEM) is closer to 1, the lithium-transition metal compositeoxide particles are made of small number of primary particles. In viewof durability, it is preferable that ²D₅₀/²D_(SEM) be in a range of 1 to4. In view of power output density, it is preferable that ²D₅₀/²D_(SEM)be 3 or less, particularly preferably 2.5 or less.

Further, the 50% particle size ²D₅₀ of the lithium-transition metalcomposite oxide particles is, for example, 1 μm or more, and preferably1.5 μm or more. The 50% particle size ²D₅₀ is, for example, 21 μm orless, preferably 5.5 μm or less, and more preferably 3 μm or less.

The 50% particle size ²D₅₀ is determined as a particle sizecorresponding to a cumulative percentage of 50% from the smallerparticle size side in the volume-based cumulative particle sizedistribution measured under wet conditions using a laser diffractionparticle size distribution analyzer. Similarly, the 90% particle size²D₉₀ and 10% particle size ²D₁₀ described below are determined asparticle sizes corresponding to cumulative percentages of 90% and 10%,respectively, from the smaller particle size side.

In the lithium-transition metal composite oxide particles, the ratio²D₉₀/²D₁₀ of 90% particle size ²D₉₀ to 10% particle size ²D₁₀ involume-based cumulative particle size distribution is, for example, 4 orless, preferably 3 or less, and more preferably 2.5 or less in view ofoutput characteristics.

The lithium-transition metal composite oxide constituting thelithium-transition metal composite oxide particles has a compositionrepresented by the above formula (1). Further, it is preferable that thelithium-transition metal composite oxide have a layered structure.Examples of lithium-transition metal composite oxides having acomposition represented by formula (1) and having a layered structureinclude lithium-nickel composite oxides andlithium-nickel-cobalt-manganese composite oxides.

In formula (1), in terms of output characteristics, it is preferablethat p satisfy 1.1≤p≤1.2. In view of productivity, it is preferable thatx satisfy 0.3≤x<0.5. In view of material cost, it is preferable that ysatisfy 0<y≤0.33, and in view of charge/discharge capacity and outputcharacteristics, it is preferable that z satisfy 0<z≤0.4. In addition,it is preferable that x:z is 3:1 to 1:1, and more preferably 2:1 to 1:1.

In the positive electrode active material, the lithium-transition metalcomposite oxide particles obtained in the method of producing asdescribed above may be doped with an element other than the elementsforming the lithium-transition metal composite oxide. Examples of anelement for doping include B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Zn,Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Ta, W, and Bi.Examples of compounds used for doping with these elements include oxidesand fluorides containing at least one element selected from the groupconsisting of these elements, and Li composite oxides thereof. Theamount of doping may be, for example, in a range of 0.005 mol % to 10mol % with respect to the lithium-transition metal composite oxideparticles, for example.

In the positive electrode active material, the lithium-transition metalcomposite oxide particles obtained in the method of producing asdescribed above may include core particles containing alithium-transition metal composite oxide and a deposit disposed on thecore particle surface. The deposit should be disposed on at least aportion of the core particle surface, and is preferably disposed in aregion of 1% or more of the surface area of the core particles. Thecomposition of the deposit is suitably selected in accordance with thepurpose and the like, and examples thereof include oxides and fluoridescontaining at least one kind selected from the group consisting of B,Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Zn, Sr, Y, Zr, Nb, Mo, In, Sn, Ba,La, Ce, Nd, Sm, Eu, Gd, Ta, W, and Bi, as well as Li-composite oxidesthereof. The content of deposit may be, for example, may be in a rangeof 0.03 mass % to 10 mass %, preferably 0.1 mass % to 2 mass %, of thelithium-transition metal composite oxide particles.

In the lithium-transition metal composite oxide, in view of the initialefficiency in a nonaqueous electrolyte secondary battery, the disorderof nickel element determined by X-ray diffractometry is preferably 4.0%or less, more preferably 2.0% or less, and still more preferably 1.5% orless. The expression “disorder of nickel element” in the presentspecification refers to chemical disorder of nickel ions generated in asite of transition metal ions. In a lithium-transition metal compositeoxide having a layered structure, such a disorder is typically anexchange between lithium ions that occupies the site represented by 3bwhen expressed in the Wyckoff symbol (i.e., 3b site, the same applieshereinafter) and transition metal ions that occupies the 3a site. Thesmaller disorder of nickel element is, the more initial efficiency isimproved, and thus is more preferable.

When applied to a positive electrode of a nonaqueous electrolytesecondary battery, a positive electrode active material produced by themethod of producing according to one embodiment of the presentdisclosure can provide a nonaqueous electrolyte secondary battery thatcan achieve both good output characteristics and good durability. Apositive electrode active material can be contained in a positiveelectrode active material layer disposed on a current collector toconstitute a positive electrode. That is, the present invention furtherincludes: an electrode for a nonaqueous electrolyte secondary batterythat includes a positive electrode active material produced by theproduction method described above; and a nonaqueous electrolytesecondary battery including the electrode.

Electrode for Nonaqueous Electrolyte Secondary Battery

An electrode for a nonaqueous electrolyte secondary battery includes acurrent collector and a positive electrode active material layer that isdisposed on the current collector and contains the positive electrodeactive material for a nonaqueous electrolyte secondary battery describedabove. A nonaqueous electrolyte secondary battery including such anelectrode can achieve both high durability and high outputcharacteristics.

Examples of materials for the current collector include aluminum,nickel, and stainless steel. The positive electrode active materiallayer can be formed as below. A positive electrode mixture obtained bymixing the above positive electrode active material, an electricallyconductive material, a binder, and the like with a solvent is appliedonto a current collector, followed by a drying treatment, apressurization treatment, and the like. Examples of electricallyconductive materials include natural graphite, artificial graphite, andacetylene black. Examples of binders include polyvinylidene fluoride,polytetrafluoroethylene, and polyamide acrylic resin.

Nonaqueous Electrolyte Secondary Battery

A nonaqueous electrolyte secondary battery includes the electrode for anonaqueous electrolyte secondary battery described above. In addition tothe electrode for a nonaqueous electrolyte secondary battery, thenonaqueous electrolyte secondary battery further includes a negativeelectrode for a nonaqueous secondary battery, a nonaqueous electrolyte,a separator, and the like. As the negative electrode, nonaqueouselectrolyte, separator, and the like in the nonaqueous electrolytesecondary battery, those for a nonaqueous electrolyte secondary batterydescribed in JP 2002-075367 A, JP 2011-146390 A, JP 2006-12433 A, andthe like (the disclosures of which are incorporated herein by referencein their entirety) may be suitably used, for example.

EXAMPLES

Examples of the present invention will be described below in detail.

First, methods of measuring physical properties in examples andcomparative examples in the below will be described.

The value of ¹D₁₀ and ²D₁₀, ¹D₅₀ and ²D₅₀, and ¹D₉₀ and ²D₉₀ weredetermined by, with use of a laser diffraction particle sizedistribution analyzer (SALD-3100 manufactured by Shimadzu Corporation),measuring volume-based cumulative particle size distribution, andcalculating the value of each of ¹D₁₀ and ²D₁₀, ¹D₅₀ and ²D₅₀, and ¹D₉₀and ²D₉₀ corresponding to the respective cumulative percentages from thesmaller particle size side were determined.

The average particle size ¹D_(SEM) and ²D_(SEM) based on electronmicroscopic observation was determined as follows. In an image observedat a magnification of 1,000 to 10,000 using a scanning electronmicroscope (SEM), 100 particles having recognizable outlines wereselected, and the equivalent spherical diameters of the selectedparticles were calculated using an image processing software (Image J).The arithmetic average of the obtained equivalent spherical diameterswas determined as D_(SEM).

The value of elemental nickel disorder (amount of Ni disorder) wasdetermined by X-ray diffractometry as below. The X-ray diffractionspectrum of obtained lithium-transition metal composite oxide particleswas measured using a CuKα ray under conditions of a tube current of 40mA and a tube voltage of 40 kV. With the composition model beingexpressed as Li_(1-d)Ni_(d)MeO₂ (wherein Me is transition metals otherthan nickel in the lithium-transition metal composite oxide), based onthe obtained X-ray diffraction spectrum, the structure of thelithium-transition metal composite oxide particles was optimized byRietveld analysis using RIETAN-2000 software. The percentage of dcalculated as a result of structural optimization was determined as theamount of Ni disorder.

Example 1 Seed Formation Step

First, 10 kg of water was charged in a reaction tank, an aqueous ammoniasolution was added into water while stirring water, and the ammonium ionconcentration was adjusted to 1.8 mass %. The temperature in the tankwas set at 25° C., and a nitrogen gas was circulated in the tank tomaintain the oxygen concentration of the inner space of the reactiontank at 10 vol % or less. A 25 mass % aqueous sodium hydroxide solutionwas added to water in the reaction tank, and the pH value of thesolution in the tank was adjusted to 13.5 or more. Next, a nickelsulfate solution, a cobalt sulfate solution, and a manganese sulfatesolution were mixed to prepare a mixed aqueous solution having a molarratio of 1:1:1. The mixed aqueous solution was added to the solution inthe reaction tank until the solute content reached 4 mol, and, whilecontrolling the pH value of the reaction solution at 12.0 or more with asodium hydroxide solution, seed formation was performed.

Crystallization Step

After the seed formation step, the temperature in the tank wasmaintained at 25° C. or more until the completion of the crystallizationstep. In addition, a mixed aqueous solution having a solute content of1,200 mol was prepared and added to the reaction tank simultaneouslywith an aqueous ammonia solution while maintaining the ammonium ionconcentration in the solution at 2,000 ppm or more over 5 hours or moreso that no additional seed formation would take place in the reactiontank. During the reaction, the pH value of the reaction solution wascontrolled to be maintained in a range of 10.5 to 12.0 with a sodiumhydroxide solution. Sampling was successively performed during thereaction, and the addition was completed when the D₅₀ of the compositehydroxide particles reached about 4.5 μm.

Next, the product was washed with water, filtered, and dried, so thatcomposite hydroxide particles are obtained. The obtained hydroxideprecursor was subjected to a heat treatment at 300° C. for 20 hours inthe ambient atmosphere, thereby obtaining a composite oxide having thefollowing properties: composition ratio Ni/Co/Mn=0.33/0.33/0.33,¹D₁₀=3.4 μm, ¹D₅₀=4.5 μm, ¹D₉₀=6.0 μm, ¹D₉₀/¹D₁₀=1.8.

Synthesis Step

The obtained composite oxide and lithium carbonate were mixed such thatLi/(Ni+Co+Mn) satisfies 1.15 to obtain a raw material mixture. Theobtained raw material mixture was calcined in air at 925° C. for 7.5hours and then calcined at 1,030° C. for 6 hours to obtain a sinteredbody. The obtained sintered body was crushed, subjected to a dispersiontreatment once using a jet mill in which the feed pressure was adjustedto 0.2 MPa and the grinding pressure was adjusted to 0.1 MPa so that theprimary particles is prevented from being ground, and then dry-sieved toobtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.15)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size ²D_(SEM) based onelectron microscopic observation: 2.8 μm, ²D₁₀=2.9 μm, ²D₅₀=5.0 μm,²D₉₀=7.9 μm, ratio ²D₅₀/²D_(SEM) of ²D₅₀ to average particle size²D_(SEM): 1.8, ratio ²D₉₀/²D₁₀ in particle size distribution: 2.7,amount of Ni disorder: 0.6%. The physical property values of theobtained lithium-transition metal composite oxide particles are shown inTable 1, and an SEM image thereof is shown in FIG. 1.

Example 2

Under the same conditions as in Example 1 except that the timing of thecompletion of addition of a mixed aqueous solution in thecrystallization step was changed to the time where the value of D₅₀ ofcomposite hydroxide particles reached about 3.0 μm, first compositeoxide particles having the following properties was obtained:composition ratio Ni/Co/Mn=0.33/0.33/0.33, ¹D₁₀=2.2 μm, ¹D₅₀=3.0 μm,¹D₉₀=4.1 μm, ¹D₉₀/¹D₁₀=1.9. The obtained first composite oxide particlesand lithium carbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.05 toobtain a raw material mixture. The obtained raw material mixture wascalcined in air at 925° C. for 7.5 hours and then calcined at 1,030° C.for 6 hours to obtain a sintered body. The obtained sintered body wascrushed, subjected to a dispersion treatment in a ball mill made ofresin for 30 minutes, and then dry-sieved to obtain a powder. Theobtained powder and lithium carbonate were mixed so that Li/(Ni+Co+Mn)becomes 1.17 and calcined in air at 700° C. for 10 hours to obtain asintered body. The obtained sintered body was crushed, subjected to adispersion treatment in a ball mill made of resin for 30 minutes, andthen dry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size ²D_(SEM): 1.2 μm,²D₁₀=1.4 μm, ²D₅₀=3.2 μm, ²D₉₀=5.1 μm, ratio ²D₅₀/²D_(SEM) of ²D₅₀ toaverage particle size ²D_(SEM): 2.7, ratio ²D₉₀/²D₁₀ in particle sizedistribution: 3.6, amount of Ni disorder: 1.7%. The physical propertyvalues of the obtained lithium-transition metal composite oxideparticles are shown in Table 1.

Example 3

First composite oxide particles were obtained under the same conditionsas in Example 2. The obtained first composite oxide particles andlithium carbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.05 toobtain a raw material mixture. The obtained raw material mixture wascalcined in air at 925° C. for 7.5 hours and then calcined at 1,030° C.for 6 hours to obtain a sintered body. The obtained sintered body wascrushed, subjected to a dispersion treatment in a ball mill made ofresin for 30 minutes, and then dry-sieved to obtain a powder. Theobtained powder and lithium carbonate were mixed at Li/(Ni+Co+Mn)=1.17and calcined in air at 900° C. for 10 hours to obtain a sintered body.The obtained sintered body was crushed, subjected to a dispersiontreatment in a ball mill made of resin for 30 minutes, and thendry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size ²D_(SEM): 1.2 μm,²D₁₀=1.5 μm, ²D₅₀=3.3 μm, ²D₉₀=5.1 μm, ratio ²D₅₀/²D_(SEM) of ²D₅₀ toaverage particle size ²D_(SEM): 2.8, ratio ²D₉₀/²D₁₀ in particle sizedistribution: 3.4, amount of Ni disorder: 0.9%. The physical propertyvalues of the obtained lithium-transition metal composite oxideparticles are shown in Table 1, and an SEM image thereof is shown inFIG. 2.

Example 4

First composite oxide particles were obtained under the same conditionsas in Example 2. The obtained first composite oxide particles andlithium carbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.05 toobtain a raw material mixture. The obtained raw material mixture wascalcined in air at 925° C. for 7.5 hours and then calcined at 1,030° C.for 6 hours to obtain a sintered body. The obtained sintered body wascrushed, subjected to a dispersion treatment in a ball mill made ofresin for 30 minutes, and then dry-sieved to obtain a powder. Theobtained powder and lithium carbonate were mixed so that Li/(Ni+Co+Mn)becomes 1.17 and calcined in air at 900° C. for 10 hours to obtain asintered body. The obtained sintered body was crushed, subjected to adispersion treatment twice using a jet mill with the feed pressureadjusted to 0.4 MPa and the grinding pressure adjusted to 0.55 MPa so asto prevent the primary particles from being ground, and then dry-sievedto obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.17)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size ²D_(SEM): 1.4 μm,²D₁₀=1.1 μm, ²D₅₀=1.9 μm, ²D₉₀=2.8 μm, ratio ²D₅₀/²D_(SEM) of ²D₅₀ toaverage particle size ²D_(SEM): 1.4, ratio ²D₉₀/²D₁₀ in particle sizedistribution: 2.5, amount of Ni disorder: 1.0%. The physical propertyvalues of the obtained lithium-transition metal composite oxideparticles are shown in Table 1, and an SEM image thereof is shown inFIG. 3.

Example 5

Under the same conditions as in Example 1 except that the timing of thecompletion of addition of a mixed aqueous solution in thecrystallization step was changed to the time where the D₅₀ of compositehydroxide particles reached 9.9 μm, first composite oxide particleshaving the following properties were obtained: composition ratioNi/Co/Mn=0.33/0.33/0.33, ¹D₁₀=8.6 μm, ¹D₅₀=9.9 μm, ¹D₉₀=12.7 μm,¹D₉₀/¹D₁₀=1.5. The obtained first composite oxide particles and lithiumcarbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.05 to obtain a rawmaterial mixture. The obtained raw material mixture was calcined in airat 925° C. for 7.5 hours and then calcined at 1,080° C. for 6 hours toobtain a sintered body. The obtained sintered body was crushed,subjected to a dispersion treatment in a ball mill made of resin for 10minutes, and then dry-sieved to obtain a powder. The obtained powder andlithium carbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.14 andcalcined in air at 900° C. for 10 hours to obtain sintered body. Theobtained sintered body was crushed, subjected to a dispersion treatmentin a ball mill made of resin for 10 minutes, and then dry-sieved toobtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.14)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size ²D_(SEM): 6.8 μm,²D₁₀=7.6 μm, ²D₅₀=10.4 μm, ²D₉₀=16.4 μm, ratio ²D₅₀/²D_(SEM) of ²D₅₀ toaverage particle size ²D_(SEM): 1.5, ratio ²D₉₀/²D₁₀ in particle sizedistribution: 2.2, amount of Ni disorder: 1.1%. The physical propertyvalues of the obtained lithium-transition metal composite oxideparticles are shown in Table 1, and an SEM image thereof is shown inFIG. 4.

Example 6

First composite oxide particles were obtained under the same conditionsas in Example 2. T The obtained first composite oxide particles andlithium carbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.05 toobtain a raw material mixture. The obtained raw material mixture wascalcined in air at 925° C. for 7.5 hours and then calcined at 1,030° C.for 6 hours to obtain a sintered body. The obtained sintered body wascrushed, subjected to a dispersion treatment in a ball mill made ofresin for 10 minutes, and then dry-sieved to obtain a powder. Theobtained powder and lithium carbonate were mixed so that Li/(Ni+Co+Mn)becomes 1.14 and calcined in air at 900° C. for 10 hours to obtain asintered body. The obtained sintered body was crushed, subjected to adispersion treatment in a ball mill made of resin for 10 minutes, andthen dry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.14)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size ²D_(SEM): 1.25 μm,²D₁₀=2.7 μm, ²D₅₀=4.5 μm, ²D₉₀=6.7 μm, ratio ²D₅₀/²D_(SEM) of ²D₅₀ toaverage particle size ²D_(SEM) of primary particles: 3.6, ratio²D₉₀/²D₁₀ in particle size distribution: 2.5, amount of Ni disorder:1.0%. The physical property values of the obtained lithium-transitionmetal composite oxide particles are shown in Table 1, and an SEM imagethereof is shown in FIG. 5.

Comparative Example 1

Under the same conditions as in Example 1 except that, during thereaction in the crystallization step, a seed slurry prepared in the seedformation step to the reaction tank was added several times, and thetiming of the completion of addition of a mixed aqueous solution waschanged to the time at which the D₅₀ of composite hydroxide particlesreached 5.0 μm, a composite oxide having the following properties wasobtained: composition ratio Ni/Co/Mn=0.33/0.33/0.33, ¹D₁₀=2.4 μm,¹D₅₀=5.0 μm, ¹D₉₀=12.2 μm, ¹D₉₀/¹D₁₀=5.1. The obtained composite oxideand lithium carbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.05 toobtain a raw material mixture. The obtained raw material mixture wascalcined in air at 925° C. for 7.5 hours and then calcined at 1,030° C.for 6 hours to obtain a sintered body. The obtained sintered body wascrushed, subjected to a dispersion treatment in a ball mill made ofresin for 10 minutes, and then dry-sieved to obtain a powder. Theobtained powder and lithium carbonate were mixed so that Li/(Ni+Co+Mn)becomes 1.14 and calcined in air at 900° C. for 10 hours to obtain asintered body. The obtained sintered body was crushed, subjected to adispersion treatment in a ball mill made of resin for 10 minutes, andthen dry-sieved to obtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.14)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size ²D_(SEM): 3.65 μm,²D₁₀=2.5 μm, ²D₅₀=7.0 μm, ²D₉₀=13.5 μm, ratio ²D₅₀/²D_(SEM) of ²D₅₀ toaverage particle size of primary particles: 1.9, ratio ²D₉₀/²D₁₀ inparticle size distribution: 5.4, amount of Ni disorder: 0.9%. Thephysical property values of the obtained lithium-transition metalcomposite oxide particles are shown in Table 1, and an SEM image thereofis shown in FIG. 6.

Comparative Example 2

First composite oxide particles were obtained under the same conditionsas in Example 2. The obtained first composite oxide particles andlithium carbonate were mixed so that Li/(Ni+Co+Mn) becomes 1.15 toobtain a raw material mixture. The obtained raw material mixture wascalcined in air at 950° C. for 15 hours to obtain a sintered body. Theobtained sintered body was crushed, subjected to a dispersion treatmentin a ball mill made of resin for 10 minutes, and then dry-sieved toobtain a powder.

As a result, lithium-transition metal composite oxide particlesrepresented by the composition formula:Li_(1.15)Ni_(0.33)Co_(0.33)Mn_(0.33)O₂ and having the followingproperties were obtained: average particle size ²D_(SEM): 0.49 μm,²D₁₀=3.0 μm, ²D₅₀=4.4 μm, ²D₉₀=7.6 μm, ratio ²D₅₀/²D_(SEM) of ²D₅₀ toaverage particle size ²D_(SEM): 9.0, ratio ²D₉₀/²D₁₀ in particle sizedistribution: 2.5, amount of Ni disorder: 0.9%. The physical propertyvalues of the obtained lithium-transition metal composite oxideparticles are shown in Table 1, and an SEM image thereof is shown inFIG. 7.

TABLE 1 Compositon ²D_(SEM) ²D₁₀ ²D₅₀ ²D₉₀ Amount of Ni ¹D₉₀/¹D₁₀ p x yz (μm) (μm) (μm) (μm) ²D₅₀/²D_(SEM) ²D₉₀/²D₁₀ disorder (%) Example 1 1.81.15 0.33 0.33 0.33 2.8 2.9 5.0 7.9 1.8 2.7 0.6 Example 2 1.9 1.17 0.330.33 0.33 1.2 1.4 3.2 5.1 2.7 3.6 1.7 Example 3 1.9 1.17 0.33 0.33 0.331.2 1.5 3.3 5.1 2.8 3.4 0.9 Example 4 1.9 1.17 0.33 0.33 0.33 1.4 1.11.9 2.8 1.4 2.5 1.0 Example 5 1.5 1.14 0.33 0.33 0.33 6.8 7.6 10.4 16.41.5 2.2 1.1 Example 6 1.9 1.14 0.33 0.33 0.33 1.25 2.7 4.5 6.7 3.6 2.51.0 Comparative 5.1 1.14 0.33 0.33 0.33 3.65 2.5 7.0 13.5 1.9 5.4 0.9Example 1 Comparative 1.9 1.15 0.33 0.33 0.33 0.49 3.0 4.4 7.6 9.0 2.50.9 Example 2

Lithium-transition metal oxide particles produced by the method ofproducing described above are a single particle or particles composed ofa small number of primary particles, and thus can be efficientlyproduced without performing another heat treatment after grinding theobtained lithium transition metal oxide to adjust its particle size.

Lithium-transition metal composite oxide particles produced by theproduction method described above has ²D₅₀/²D_(SEM) and ²D₉₀/²D₁₀ thatare smaller compared with those in Comparative Examples 1 and 2.Accordingly, they are a single particle or are particles composed of asmall number of primary particles, and have a uniform particle size. Inparticular, in Examples 3 and 4, the value of ²D_(SEM) is relativelysmall, the value of ²D₅₀/²D_(SEM) is small, the value of ²D₉₀/²D₁₀ issmall, and the amount of Ni disorder is small. Therefore, applying suchparticles to a positive electrode active material of a nonaqueouselectrolyte secondary battery allows for providing a nonaqueouselectrolyte secondary battery having good output characteristic anddurability.

It is to be understood that although the present invention has beendescribed with regard to preferred embodiments thereof, various otherembodiments and variants may occur to those skilled in the art, whichare within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

Although the present disclosure has been described with reference toseveral exemplary embodiments, it is to be understood that the wordsthat have been used are words of description and illustration, ratherthan words of limitation. Changes may be made within the purview of theappended claims, as presently stated and as amended, without departingfrom the scope and spirit of the disclosure in its aspects. Although thedisclosure has been described with reference to particular examples,means, and embodiments, the disclosure may be not intended to be limitedto the particulars disclosed; rather the disclosure extends to allfunctionally equivalent structures, methods, and uses such as are withinthe scope of the appended claims.

One or more examples or embodiments of the disclosure may be referred toherein, individually and/or collectively, by the term “disclosure”merely for convenience and without intending to voluntarily limit thescope of this application to any particular disclosure or inventiveconcept. Moreover, although specific examples and embodiments have beenillustrated and described herein, it should be appreciated that anysubsequent arrangement designed to achieve the same or similar purposemay be substituted for the specific examples or embodiments shown. Thisdisclosure may be intended to cover any and all subsequent adaptationsor variations of various examples and embodiments. Combinations of theabove examples and embodiments, and other examples and embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

In addition, in the foregoing Detailed Description, various features maybe grouped together or described in a single embodiment for the purposeof streamlining the disclosure. This disclosure may not be interpretedas reflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter may be directed toless than all of the features of any of the disclosed embodiments. Thus,the following claims are incorporated into the Detailed Description,with each claim standing on its own as defining separately claimedsubject matter.

The above disclosed subject matter shall be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments which fall within thetrue spirit and scope of the present disclosure. Thus, to the maximumextent allowed by law, the scope of the present disclosure may bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

All publications, patent applications, and technical standards mentionedin this specification are herein incorporated by reference to the sameextent as if each individual publication, patent application, ortechnical standard was specifically and individually indicated to beincorporated by reference.

1. A method of producing a positive electrode active material for anonaqueous electrolyte secondary battery, comprising: providingnickel-containing composite oxide particles having a ratio ¹D₉₀/¹D₁₀ ofa 90% particle size ¹D₉₀ to a 10% particle size ¹D₁₀ in volume-basedcumulative particle size distribution of 3 or less; mixing the compositeoxide particles and a lithium compound to obtain a first mixture;subjecting the first mixture to a first heat treatment at a firsttemperature and a second heat treatment at a second temperature higherthan the first temperature to obtain a first heat-treated material; anddissociating from the first heat-treated material the positive electrodeactive material, wherein the positive electrode active materialcomprises lithium-transition metal composite oxide particles beingsingle particles, wherein the lithium-transition metal composite oxideparticles have a ratio ²D₉₀/²D₁₀ of a 90% particle size ²D₉₀ to a 10%particle size ²D₁₀ in volume-based cumulative particle size distributionis 4 or less, and wherein a molar ratio of nickel in a composition ofthe lithium-transition metal composite oxide to a total molar number ofmetals other than lithium is 0.3 to 0.6.
 2. The method according toclaim 1, wherein the lithium-transition metal composite oxide furthercontains cobalt and a molar ratio of cobalt in the composition to atotal molar number of metals other than lithium is 0.4 or less.
 3. Themethod according to claim 1, wherein the lithium-transition metalcomposite oxide further contains at least one of Mn or Al and a molarratio of total molar number of Mn and Al in the composition to a totalmolar number of metals other than lithium is 0.5 or less.
 4. The methodaccording to claim 1, wherein a molar ratio of lithium in thecomposition to a total molar number of metals other than lithium is 1.0to 1.3.
 5. The method according to claim 1, wherein a molar ratio ofoxygen in the composition to a total molar number of metals other thanlithium is 1.9 to 2.1.
 6. The method according to claim 1, wherein thelithium-transition metal composite oxide particles have a compositionrepresented by the following formula (1):Li_(p)Ni_(x)Co_(y)M¹ _(z)O_(2+α)  (1) wherein p, x, y, z, and a satisfy1.0≤p≤1.3, 0.3≤x≤0.6, 0≤y≤0.4, 0≤z≤0.5, x+y+z=1, and −0.1≤α≤0.1, and M¹represents at least one of Mn and Al.
 7. The method according to claim1, wherein the first temperature is in a range of 850° C. to 950° C.,and the second temperature is in a range of 980° C. to 1,100° C.
 8. Themethod according to claim 1, further comprising: mixing the positiveelectrode active material dissociated from the first heat-treatedmaterial and a lithium compound to obtain a second mixture; andsubjecting the second mixture to a heat treatment to obtain a secondheat-treated material.
 9. The method according to claim 7, furthercomprising: mixing the positive electrode active material dissociatedfrom the first heat-treated material and a lithium compound to obtain asecond mixture; and subjecting the second mixture to a heat treatment toobtain a second heat-treated material.
 10. The method according to claim1, wherein the composite oxide particles have a 50% particle size ¹D₅₀in volume-based cumulative particle size distribution is in a range of 1μm to 4 μm, and the lithium-transition metal composite oxide particlesare configured such that the 50% particle size ²D₅₀ in volume-basedcumulative particle size distribution is in a range of 1 μm to 3 μm. 11.The method according to claim 7, wherein the composite oxide particleshave a 50% particle size ¹D₅₀ in volume-based cumulative particle sizedistribution is in a range of 1 μm to 4 μm, and the lithium-transitionmetal composite oxide particles are configured such that the 50%particle size ²D₅₀ in volume-based cumulative particle size distributionis in a range of 1 μm to 3 μm.
 12. The method according to claim 8,wherein the composite oxide particles have a 50% particle size ¹D₅₀ involume-based cumulative particle size distribution is in a range of 1 μmto 4 μm, and the lithium-transition metal composite oxide particles areconfigured such that the 50% particle size ²D₅₀ in volume-basedcumulative particle size distribution is in a range of 1 μm to 3 μm. 13.The method according to claim 9, wherein the composite oxide particleshave a 50% particle size ¹D₅₀ in volume-based cumulative particle sizedistribution is in a range of 1 μm to 4 μm, and the lithium-transitionmetal composite oxide particles are configured such that the 50%particle size ²D₅₀ in volume-based cumulative particle size distributionis in a range of 1 μm to 3 μm.
 14. The method according to claim 6,wherein p in formula (1) satisfies 1.1≤p≤1.2.